In the exploration and development of offshore petroleum reserves, it is sometimes necessary to erect platforms located miles off shore. These platforms form a base on which drilling, exploration and storage activities can occur. Some of these platforms have legs or other types of support structure which extend down into the water. To transport men and material to and from these platforms, it is necessary to dock vessels alongside. In some situations, these vessels are small. In others, the vessels are quite large and contact between these larger vessels and the platform leg structure can weaken or otherwise damage either the structure or the vessel itself.
To protect these platforms from damage due to contact by vessels operating near the platforms, systems have been designed which are attached to the platform adjacent the water level and operate to fend off vessels and absorb shocks from vessels coming into contact with the platform.
One system which has been used for years in the industry has been known as the Lawrence Allison system. This system utilizes a vertically standing piece of pipe or other structural member which is supported from the platform at the water level. The pipe typically has its upper end supported from the leg of the platform at a position above the high tide level and the lower end connected to the platform at a position below the low tide level. The system utilizes a plurality of rubber vehicle tires with the vertically standing structural member exiting through the center of the tires to form a stack of tires which absorb shocks from contact with vessels. Some of these Lawrence Allison systems leave the outer surfaces of tires exposed, and some have a cylindrical metal skin or can supported around the outside of the tires and spaced away from the central support by the tires. In the latter case, the tires resiliently separate the outer contact skin from the inner central support.
In other prior art systems, the outer can or contact surface are resiliently separated from the central structural support by a preformed rubber element. In one such system, the outer protective shield or can and the central support are coaxially positioned. A solid rubber element extends the length of the outer shield and occupies less than 360.degree. but at least 180.degree. of the annular space formed between the outer shield and the central support. In these devices, the rubber element has a constant radial thickness positioned in the annular space on the side from which contact with vessels normally occurs.
Although prior art bumper systems have performed satisfactorily, in many ways unappreciated by the industry, their design has contained aspects which were redundant and which added to the overall costs of the systems. These systems, for example, failed to appreciate and/or accommodate into the design cost savings and size reductions which could be accomplished if the limited directions from which contact forces are applied to the system are taken into account. Further, these systems utilized complicated manufacturing and fabrication techniques which were unnecessary. In the past, these systems have been expensive to manufacture and install and as a consequence have not proven entirely satisfactory.